Coffee has been having a pretty good run lately.
The World Health Organization recently downgraded a warning that previously suggested everyone's favorite morning beverage may contribute to cancer risk. Experts now say there's actually no evidence that coffee causes cancer, though they do warn that drinking any very hot beverage might be linked to cancer of the esophagus.
What's more, late last year, a major report funded by the National Institutes of Health found that regular consumption of coffee was associated with lower risk of total mortality as well as mortality caused by cardiovascular disease.
But new research says those health reports still don't make coffee a miracle drink. While there's consensus from researchers and non-morning people everywhere that the caffeine in coffee boosts alertness and focus, a new study shows those benefits pretty much disappear if you're too tired.
In other words, your morning cup is no panacea for bad sleep habits. In the study, caffeine's cognitive and mood benefits waned after people went just three days without getting enough sleep.
“Caffeine is not sufficient to prevent performance decline over multiple days of restricted sleep.”- Tracy Jill Doty, a research scientist at Walter Reed Army Institute of Research
"The data from this study suggests that the same effective daily dose of caffeine is not sufficient to prevent performance decline over multiple days of restricted sleep," the study's lead author Tracy Jill Doty, a research scientist at Walter Reed Army Institute of Research, said in a press release.
Listen closely and you can hear the coffee cups of dozy java-lovers everywhere shattering on the floor.
The study followed 48 individuals whose sleep was restricted to five hours per night for five nights. Each following day, the individuals were either given a 200 mg caffeine pill or a placebo pill, followed by a series of tests.
Scores on tests measuring reaction time and mood were higher for the caffeinated group for the first two days, but NOT for the the days after that.
By the third day of the study, overall ratings for happiness were lower for the people who had gotten the caffeine compared with those who had not. And by the end of the experiment, those in the caffeine group rated themselves as more annoyed than those who had not had caffeine.
The study was presented earlier this week at a meeting of sleep medicine physicians, researchers and professionals in Denver, Colorado.
The good news is that reaping the alertness- and performance-boosting benefits of caffeinated coffee is still possible any day -- as long as you haven't gotten more than three poor nights of sleep in a row.
Bottom line: If you haven't slept well in a few days, a nap (and a good night's shuteye!) is going to do you a lot more good than another cup of coffee.
Sarah DiGiulio is The Huffington Post’s sleep reporter. You can contact her at firstname.lastname@example.org.